The present invention relates to a soldering method and soldering apparatus for dropping molten or semi-molten solder (hereinafter referred to simply as molten solder) on a workpiece to effect soldering.
There is proposed a soldering apparatus for automatically applying molten solder onto a desired point or area of a workpiece, such as a printed circuit board, wherein a conical pot is used for melting a solid solder (Japanese Patent Publication (KOKOKU) No. 46-34209 (1971)). A rod-shaped solder is cut and fed to the conical pot to be melted therein and the molten solder is allowed to drop onto a workpiece through a hole provided at the bottom of the pot. However, this type soldering apparatus has a problem that some portion of the solid solder drops through the hole in the unmelted state while the other portion of the solder is dropped in the overheated condition, since it is impossible to retain the whole solid solder for a constant time, resulting in uneven and unreliable soldering.
There is also proposed a soldering apparatus having a conical melting pot provided with a needle valve at the bottom of the pot (Unexamined Japanese Utility Model Publication (KOKAI) No. 50-77427 (1975)). In this known apparatus, a molten mass of solder is contained in the conical melting pot, and a constant volume of the molten solder is allowed to drop through the needle valve. However, due to surface tension of the molten solder, it becomes impossible to control the volume of dropping molten solder precisely particularly when the volume of molten solder to be applied onto the workpiece is relatively small, as is the case where the workpiece is a printed circuit board.
In order to solve the aforementioned problems of the known apparatuses, the present inventor has previously proposed an improvement in soldering in my earlier Japanese Patent Application No. 61-110505 (1986) which is published as JP-A-62-270272. According to my previous proposal, a solder melting pot is formed by plural trowel members which engage with each other to hold a solid solder tip or piece for a pre-set time to melt the same and then they are separated to allow the molten solder to drop onto a desired point or area of a workpiece.
These conventional methods must prevent so-called xe2x80x9cknotty or tubercled solderingxe2x80x9d by allowing additional heating the soldering point to enable excellent flow of molten solder to the soldering point after supplying molten solder to the soldering point. In this case, the trowel members are separated and raised to allow the molten solder to drop onto the soldering point, and the trowel members are again lowered to come close to the same desired point right after dropping.
However, such a process leads to the deteriorated process efficiency when a plurality of desired points are to be soldered. That is, the time duration for supplying the molten solder and the time duration for additional heating are required with respect to one point to be soldered.
Further, it is desirable to preheat a point to be soldered before supplying the molten solder. It can be considered to provide a preheat time during which the tip-ends (lower ends) of the trowel members are moved close to the soldering point before the trowel members are opened to drop the molten solder. However, by doing so, a time required for supplying the molten solder, an additional heating time and a preheat time therefor are required with respect to one point to be soldered. Thus, the process efficiency is further deteriorated.
In view of the above described problems, it is a first object of the present invention to provide a soldering method by which a plurality of soldering points aligned at predetermined intervals can be efficiently soldered.
It is a second object of the present invention to provide a soldering apparatus directly used for realization of such a soldering method.
According to the present invention, the first object is attained by a soldering method for soldering plural soldering points aligned at a predetermined interval; comprising the steps of forming a solder melting pot by assembling plural trowel members, each of the trowel members having a surface made of a solder repellent material at least the portion contacting with the solder; supplying a solder tip having a constant volume to said solder melting pot; and sequentially supplying the molten solder to the respective soldering points from the solder melting pot:
an improved method wherein an additional heating portion which comes close to said solder melting pot is formed to said trowel members, and wherein the soldering point to which molten solder has been supplied by prior molten solder supply operation is additionally heated during the supply operation of the molten solder to the next soldering point.
In the present invention, the trowel members are used to simultaneously perform the molten solder supply operation and the additional heating operation for the soldering point to which the molten solder was supplied by the preceeding molten solder supply operation.
In the present specification, the term xe2x80x9csoldering pointxe2x80x9d means a point or portion to be soldered of a workpiece, and includes a point or portion which will be soldered or has been soldered.
The solder melting pot may be formed by grooves formed on the opposing surfaces of the trowel members so that a cavity defining the solder melting pot is formed by these grooves when the trowel members engages with each other. Such a solder melting pot may have an opening or hole at the bottom of the pot. In this case, the opening may be closed or plugged by the upper surface or portion of the soldering point when the trowel members are lowered to come close to the soldering point. That is, the solder melting pot is formed by engaging the trowel members and the bottom opening of the pot is closed with the soldering point by lowering the trowel members assembly to come close to the soldering point. The solid solder tip is dropped to the formed and closed solder melting pot to be molten. The molten solder can be supplied to the soldering point by moving up the trowel members. Otherwise, the trowel members may be opened or separated to supply the molten solder to the soldering point.
A plurality of solder melting pots may be formed by one set of the trowel members so that each solder melting pot can simultaneously supply the molten solder to different points to be soldered by separating or raising the trowel members. For example, the solder melting pots may be provided at intervals equal to pitches of the soldering points. In this case, the additional heating portion is also formed between the solder melting pots. Alternatively, the solder melting pots may by provided at intervals as integral multiples of the same pitches. The additional heating portion is formed along the length of the multiple pitches so that it can move close to the plural soldering points ready to be soldered at the same time.
It is possible to effect the control so that a workpiece having plural soldering points can continuously move relative to the trowel member in an alignment direction of the soldering points at a fixed speed and the solder melting pot(s) can supply molten solder to predetermined points to be soldered. A workpiece may move intermittently or move while changing the speed. For example, when a plurality of solder melting pots are formed by a plurality of sets of trowel members provided along the alignment direction of the soldering points, it is preferable to periodically change the workpiece transfer speed for each of a predetermined number of soldering processes based on the number of the solder melting pots or intervals.
By providing to the trowel members a preheating portion which is placed to the opposed side of the additional heating portion with the solder melting pot therebetween, this preheating portion can be used to preheat a next soldering point to which molten solder is to be supplied. That is, the molten solder supplying operation, the additional heating operation for the soldering point to which the molten solder has been supplied by the preceeding supplying operation, and the preheating operation for a next soldering point can be simultaneously carried out.
The second object of the present invention can be attained by the provision of a soldering apparatus for soldering plural soldering points of a workpiece, the plural soldering point being aligned at a predetermined interval, comprising:
plural trowel members each having a surface made of a solder repellent material at least the portion contacting with a solder, said plural trowel members being engaged together to form a solder melting pot and separated from each other to supply the molten solder to the soldering point, a solder tip having a constant volume being supplied to said solder melting pot to be molten and then allowed to drop when said plural trowel members are separated from each other;
an additional heating portion which is formed to said trowel members in close vicinity to said solder melting pot and additionally heats an adjacent soldering point to which the molten solder has been already supplied during an operation of said solder melting pot for supplying the molten solder to the next soldering point;
a workpiece holder for relatively moving the workpiece with respect to said trowel members along an alignment direction of the plural soldering points; and
a controller for moving said workpiece holder and controlling said trowel members in synchronism with the relative movement of the workpiece, so that said trowel members are moved up and down and/or opened and closed to supply the molten solder from said solder melting pot to each of the soldering points of the workpiece.
The solder melting pot may be formed by grooves formed on the opposing surface of the trowel members. A cavity defining the solder melting pot is formed by engaging the opposing trowel members. The molten solder can be supplied to the soldering point by separating the trowel members. The solder melting pot formed by the grooves of the trowel members may have a bottom opening which can be closed or plugged with the upper portion of the soldering point when the trowel members are lowered to come close the soldering point. In this case, the molten solder can be supplied to the soldering point when the bottom of the solder melting pot is opened by moving up or opening the trowel members.
When a plurality of solder melting pots are provided to the assembly of the trowel members at the same pitches as those of the soldering points or pitches of integral multiples, plural points can be soldered all at once, thereby improving the efficiency.
When the preheating portion is provided to the trowel members so that the preheating portion is arranged on the opposed side of the additional heating portion with the solder melting pot therebetween, the molten-solder supplying operation, the additional heating operation and the preheating operation can be performed all at once.